Revised and Extended Values for Self-Diffusion Coefficients of 1-Alkyl-3-methylimidazolium Tetrafluoroborates and...

Earlier measurements of the self-diffusion coefficients of 1-alkyl-3-methylimidazolium (or [RMIM], R = alkyl) tetrafluoroborates and hexafluorophosphates have been revised and extended to 90 °C. The main changes are to D_S+ and D_S- for [HMIM][PF₆] ([C₆C₁Im][PF₆]) and D_S- for [OMIM][BF₄] ([C₈C₁Im][BF₄]). New atmospheric pressure self-diffusion, density, and conductivity data are provided for [HMIM][BF₄] ([C₆C₁Im][BF₄]). Velocity cross-correlation, distinct diffusion, and Laity resistance coefficients have been calculated. There is no evidence for ion association. A new relation between the Nernst-Einstein deviation parameter (Δ) and resistance coefficients (r_ij) is derived; Δ tends toward 0.5 when the like-ion r_ii are much smaller than the unlike-ion r_ij, i.e., when the counterion interactions dominate. [OMIM]⁺ ion salts approach this limit. Stokes-Einstein-Sutherland and Walden plots overlap almost quantitatively for [BF₄]^-, [PF₆]^-, and Cl^- salts with a common [RMIM]⁺ cation. That is, in thermodynamic states that have the same viscosity, the salt molar conductivities and hence ionic electrical mobilities of, say, [BMIM][BF₄] and [BMIM][PF₆] are almost equal, as are the corresponding Brownian or diffusive mobilities, (D_Si/RT), for the cation, and also for these three small anions.